When you are involved in recording audio, the tools you can choose from can be confusing. Among the most popular tools to buy today is a microphone preamplifier or preamp. If you look around online for preamps information, it is easy to feel overwhelmed. To help you make a more informed choice, this simple guide will break down what preamps are and how to pick your next preamp.
What is a microphone preamplifier (preamp)?
Listen to one anecdote, and you could be convinced that a preamp is akin to a magic trick that transforms any audio. Others focus more on the benefits and uses, such as adding extra life to a quiet audio source without noise polluting the track.
In reality, the preamp is a critical part of any sound recording studio. The main focus of using a preamp is to help boost a weak signal. If a weak microphone or instrument sound is ruining the end result of a recording session, you can use a preamp to bring it up to a more line-level signal. When done properly, this raises the volume to be where it is required without any needless noise or distortion being added.
Given that just about all professional recording equipment is designed to be at line-level signal (plus 4), bringing a quiet line-level signal up to the norm is very useful indeed. As you might find to your cost, though, there are so many preamps on the market that knowing what to choose can be daunting.
While many audio interfaces come with an already fitted preamp, most choose to buy a standalone preamp they can use elsewhere. Whether the preamp is pre-fitted or standalone, the main aim is to ensure you can boost gains in a recording without impacting the quality.
Before we go any further, let’s break down two key concepts quickly: line-levels and gain.
What are the key features of a preamp?
Every preamp is different in its way, both in the output it provides and the features it offers. While some preamps come with very bespoke features, it is common for all (or most) preamps to have the following features:
- Input pads, which allow you to pat down the input stage. This helps to further reduce distortion and can be excellent when recording drums and other loud instruments
- Output trimming, which allows for a manual adjustment of the output level so that you can increase gain
- Reverse polarity control, which is a vital feature if you ever need to use more than one microphone at once during the recording
- Variable input impedance, which allows for additional sonic flavoring that can transform the tone of the microphone entirely
- A phantom power level, a DC voltage of +48V, that is used to connect with the electronics found in condenser mics
Understanding line-level and gain
What is a line-level?
Signal and line levels are important; when they pair up properly, your music can sound harmonious. It can sound like a total mess when line levels are out of sync. Typically, professional line-level signals will be measured at a rating of around +4dBu. By contrast, the line-level signals on amateur or semi-pro audio equipment are usually calculated at a rating of -10dBV.
The general rule is that you interlace equipment with a +4dBu rating with equipment with +4dBu ratings and -10dBV with similar -10dBV equipment. A failure to do this tends to create a lot of needless distortion. You will either end up with a complete sound mismatch, or the sound output will be so quiet that you need to turn the volume to an unrealistic level.
Why does gain matter so much?
We have mentioned ‘gain’ above a few times. If this is a term you do not understand/know, it is quite simple. Gain is the change in voltage levels in an audio signal path. This happens when an amplifier is included. Essentially, how much is this circuit amplifying the noise output?
Gain is something that you add to your recording before any other form of processing occurs. For example, if you are using a preamp on a microphone, you would adjust the gain to match the sound level of the source. If someone is singing without enough ‘boom’ in their voice, using a preamp can increase the gain to the level required.
As you might have found to your cost, the excessive gain increase can lead to distorted sounds – it can even cause your system to overload and thus require a reset. If you go down too low, you will produce an inadequate signal-to-noise ratio.
When correctly applied, though, gain can produce extra volume without creating any distortion or noise in the background.
How much gain should I aim for?
Given that preamps increase the gain on a mic or instrument-level signal, working out how much gain you should include is challenging. Sometimes you might find you only need around 40dB of gain; other times, it could easily be double that. The answer to how much gain you should look to include comes down to two things – the microphone type you use and the instrument that is being used in front of said mic. Generally, the rules are:
- If you use a condenser mic, you might only need around 10dB to 30dB of gain. This is due to the presence of electronics already in the mic, which boosts signal output, meaning they are easier to work with
- If you use a dynamic mic, you could need anything from 50dB to 70dB and above to get the right output. It depends on the distance and volume of the instrument being used. The quieter the source, the more it needs
How does a preamp adjust output?
If you want to use a preamp, then it is very simple. The above might make it sound like you are engaging in magic, but it is nothing. Using a preamp, you can take something from a microphone or instrument-level signal and convert it into a professional line-level signal. The way that this works is to do with voltage.
A professional line-level device will use an output voltage of 1.23V. The preamp takes the mic-level signal and turns it into a usable 1.23V line-level signal. It replicates the signal and sends it through one (or numerous) amplification circuits. This then outputs this new line-level signal to all the rest of the signal chain, creating harmony in your recording device and/or audio system.
Do all preamps produce the same results?
While that would be ideal, that is not the case. The sound that comes from a preamp is going to be made up of various conditions. The presence of anything from transistors to integrated circuitry, transformers to capacitors, or any mixture of the above, can adjust the end output.
Some typical mic preamps will produce a very clear and crisp sound, avoiding any coloration in the background. Some artists use that coloration as a form of extra creative adjustment on their recordings. The cleaner the signal, the easier it typically is to adjust in post-processing.
Some others will contain transformers, which significantly alter the sound. This can produce a much punchier, fuller sound than you might be used to.
Choosing the best preamp for you
So, the major challenge is that there is no ‘right’ answer here. Every setup is different. The best preamp for you would be useless to someone with even a slightly alternative arrangement. You cannot buy an all-in-one preamp; there are different preamps for different purposes. What you can pay, the kind of microphones you use, and the applications you use in the recording will play a role in deciding for you.
You should probably do some research into the following factors, though:
- What kind of microphones are you using? Do you need a specific or hybrid mic preamp?
- What inputs and outputs do you need to pair up with your instruments and equipment?
- Do you require a single, dual, or multichannel mic preamp?
Again, there is no ‘easy’ answer – every setup needs a specific kind of preamp. Your challenge now is researching your layout enough to get an idea of what type of preamp you might need.
Of course, at MelloStudio we have quite a range of preamps of our own to offer you. Two of our most popular preamps at the moment include our Warm Audio WA-73-EQ model as well as the Warm Audio WA-273-EQ. The former is a single channel mic preamp, while the latter is a dual-channel mic preamp. Both can be exceptionally useful in different circumstances and are more than worth your time to investigate.
So, there you have it – now you know more about preamps, and why they are such a useful tool in the music industry. There is much to think about, but hopefully now you can understand what a preamp is, and what to look out for when shopping around.